code: def _test_persistence(self, config, rank, group, volatile=False):
      model = self.get_wrapped_model(
          group, cuda_first=False, config=config
      )
  
      with model.summon_full_params(volatile=False):
          model.module.embed_tokens.weight.data.fill_(42)
      with model.summon_full_params():
          # non-volatile changes are persisted
          assert torch.all(
              model.module.embed_tokens.weight.data == 42.0
          )
  
file_path: fairscale/tests/nn/data_parallel/test_fsdp_summon_full_params.py
imports: import functools
  import gc
  import unittest
  from parameterized import parameterized
  import pytest
  import torch
  from fairscale.internal.version import torch_version
  from .test_fsdp import CONFIG_OPTIONS, DistributedTest, rename_test, spawn_and_init
label_desc: Use image node_id 2 for calling the TestPersistence obj's underlying member method code with example usage: obj._test_persistence(config, rank, group, volatile) without return types